Conventionally, there is an image forming apparatus which forms an image using an image forming material which can be erased through an erasing processing. Further, the image forming apparatus forms a specific pattern such as a ground pattern as well as the image to protect the image which needs protection on, such as duplication prohibition. However, in practical processing, the erasable image forming material cannot be completely erased and may have erasing residues sometimes. If the specific pattern is erased while part of the image which needs protection is left on a paper in a duplicable state after the erasing processing, the part of the image which needs protection may be illegally duplicated.